Science posts

See science posts on page 40 below.

    • 2005
    • Steven E. Prince et al
    • Neural Correlates of Relational Memory: Successful Encoding and Retrieval of Semantic and Perceptual Associations
    • Using event-related functional magnetic resonance imaging, we identified brain regions involved in successful relational memory (RM) during encoding and retrieval for semantic and perceptual associations or in general, independent of phase and content. Participants were scanned while encoding and later retrieving associations between pairs of words (semantic RM) or associations between words and fonts (perceptual RM). Encoding success activity (ESA) was identified by comparing study-phase activity for items subsequently remembered (hits) versus forgotten (misses) and retrieval success activity (RSA) by comparing test-phase activity for hits versus misses. The study yielded three main sets of findings. First, ESA-RSA differences were found within the medial temporal lobes (MTLs) and within the prefrontal cortex (PFC). Within the left MTL, ESA was greater in the anterior hippocampus, and RSA was greater in the posterior parahippocampal cortex/hippocampus. This finding is consistent wit..
    • 2010
    • Jeffrey M. Spielberg et al
    • Trait approach and avoidance motivation: Lateralized neural activity associated with executive function
    • Motivation and executive function are both necessary for the completion of goal-directed behavior. Research investigating the manner in which these processes interact is beginning to emerge and has implicated middle frontal gyrus (MFG) as a site of interaction for relevant neural mechanisms. However, this research has focused on state motivation, and it has not examined functional lateralization. The present study examined the impact of trait levels of approach and avoidance motivation on neural processes associated with executive function. Functional magnetic resonance imaging was conducted while participants performed a color-word Stroop task. Analyses identified brain regions in which trait approach and avoidance motivation (measured by questionnaires) moderated activation associated with executive control. Approach was hypothesized to be associated with left-lateralized MFG activation, whereas avoidance was hypothesized to be associated with right-lateralized MFG activation. Resu..
    • 2012
    • Nachshon Meiran et al
    • When planning results in loss of control: intention-based reflexivity and working-memory
    • In this review, the authors discuss the seemingly paradoxical loss of control associated with states of high readiness to execute a plan, termed “intention-based reflexivity.” The review suggests that the neuro-cognitive systems involved in the preparation of novel plans are different than those involved in preparation of practiced plans (i.e., those that have been executed beforehand). When the plans are practiced, intention-based reflexivity depends on the prior availability of response codes in long-term memory (LTM). When the plans are novel, reflexivity is observed when the plan is pending and the goal has not yet been achieved. Intention-based reflexivity also depends on the availability of working-memory (WM) limited resources and the motivation to prepare. Reflexivity is probably related to the fact that, unlike reactive control (once a plan is prepared), proactive control tends to be relatively rigid.
    • 2012
    • Robert West et al
    • The temporal dynamics of medial and lateral frontal neural activity related to proactive cognitive control
    • The neural correlates of proactive cognitive control were examined in two experiments using the counting Stroop task and a computerized Blackjack task in combination with event-related brain potentials (ERPs). The primary objective of the study was to determine whether slow wave activity related to proactive control would be observed in the two tasks. Consistent with the existing literature, transient components of the ERPs (i.e., medial frontal negativity and feedback related negativity) were observed over the medial frontal region in both tasks that were related to stimulus congruency and feedback processing, respectively. The medial frontal ERPs in both tasks were modeled with a pair of equivalent current dipoles placed along the anterior to posterior axis of the cingulate. Most importantly, slow wave activity was observed that differentiated incongruent trials from congruent trials after the response in the counting Stroop task, and losses from wins and ties in the Blackjack task..
    • 2013
    • Jessica M. Phillips et al
    • A Long-Range Fronto-Parietal 5- to 10-Hz Network Predicts “Top-Down” Controlled Guidance in a Task-Switch Paradigm
    • The capacity to rapidly adjust behavioral strategies according to changing task demands is closely associated with coordinated activity in lateral and medial prefrontal cortices. Subdivisions within prefrontal cortex are implicated to encode attentional task sets and to update changing task rules, particularly when changing task demands require top-down control. Here, we tested whether these top-down processes precede stimulus processing and constitute a preparatory attentional state that functionally couples with parietal cortex. We examined this functional coupling by recording from intracranial EEG electrodes in macaques during performance of a task-switching paradigm that separates task performance that is based on controlled top-down guidance from automatic, stimulus-triggered processing modes. We identify a prefrontal-parietal network that phase synchronizes at 5–10 Hz, particularly during preparatory states that indicate top-down controlled task-processing modes. Phase r..
    • 2012
    • Kimberlee D’Ardenne et al
    • Role of prefrontal cortex and the midbrain dopamine system in working memory updating
    • Humans are adept at switching between goal-directed behaviors quickly and effectively. The prefrontal cortex (PFC) is thought to play a critical role by encoding, updating, and maintaining internal representations of task context in working memory. It has also been hypothesized that the encoding of context representations in PFC is regulated by phasic dopamine gating signals. Here we use multimodal methods to test these hypotheses. First we used functional MRI (fMRI) to identify regions of PFC associated with the representation of context in a working memory task. Next we used single-pulse transcranial magnetic stimulation (TMS), guided spatially by our fMRI findings and temporally by previous event-related EEG recordings, to disrupt context encoding while participants performed the same working memory task. We found that TMS pulses to the right dorsolateral PFC (DLPFC) immediately after context presentation, and well in advance of the response, adversely impacted context-dependent r..
    • 2012
    • Veit Stuphorn et al
    • Proactive and reactive control by the medial frontal cortex
    • Adaptive behavior requires the ability to flexibly control actions. This can occur either proactively to anticipate task requirements, or reactively in response to sudden changes. Recent work in humans has identified a network of cortical and subcortical brain region that might have an important role in proactive and reactive control. However, due to technical limitations, such as the spatial and temporal resolution of the BOLD signal, human imaging experiments are not able to disambiguate the specific function(s) of these brain regions. These limitations can be overcome through single-unit recordings in non-human primates. In this article, we describe the behavioral and physiological evidence for dual mechanisms of control in response inhibition in the medial frontal cortex of monkeys performing the stop signal or countermanding task.
    • 2015
    • Patrick S. Cooper et al
    • Theta frontoparietal connectivity associated with proactive and reactive cognitive control processes
    • Cognitive control involves both proactive and reactive processes. Paradigms that rely on reactive control have shown that frontoparietal oscillatory synchronization in the theta frequency band is associated with interference control. This study examines whether proactive control is also associated with connectivity in the same frontoparietal theta network or involves a distinct neural signature. A task-switching paradigm was used to differentiate between proactive and reactive control processes, involved in preparing to switch or repeat a task and resolving post-target interference, respectively. We confirm that reactive control is associated with frontoparietal theta connectivity. Importantly, we show that proactive control is also associated with theta band oscillatory synchronization but in a different frontoparietal network. These findings support the existence of distinct proactive and reactive cognitive control processes that activate different theta frontoparietal oscillatory ..
    • 2012
    • Todd S. Braver
    • The variable nature of cognitive control: a dual mechanisms framework
    • A core component of cognitive control – the ability to regulate thoughts and actions in accordance with internally represented behavioral goals – might be its intrinsic variability. In this article, I describe the dual mechanisms of control (DMC) framework, which postulates that this variability might arise from qualitative distinctions in temporal dynamics between proactive and reactive modes of control. Proactive control reflects the sustained and anticipatory maintenance of goal-relevant information within lateral prefrontal cortex (PFC) to enable optimal cognitive performance, whereas reactive control reflects transient stimulus-driven goal reactivation that recruits lateral PFC (plus a wider brain network) based on interference demands or episodic associations. I summarize recent research that demonstrates how the DMC framework provides a coherent explanation of three sources of cognitive control variation – intra-individual, inter-individual and between-groups..
    • 2010
    • Gregory C. Burgess et al
    • Neural Mechanisms of Interference Control in Working Memory: Effects of Interference Expectancy
    • Background A critical aspect of executive control is the ability to limit the adverse effects of interference. Previous studies have shown activation of left ventrolateral prefrontal cortex after the onset of interference, suggesting that interference may be resolved in a reactive manner. However, we suggest that interference control may also operate in a proactive manner to prevent effects of interference. The current study investigated the temporal dynamics of interference control by varying two factors – interference expectancy and fluid intelligence (gF) – that could influence whether interference control operates proactively versus reactively. Methodology/Principal Findings A modified version of the recent negatives task was utilized. Interference expectancy was manipulated across task blocks by changing the proportion of recent negative (interference) trials versus recent positive (facilitation) trials. Furthermore, we explored whether gF affected the tende..

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